Martensitic transformation and soft modes in KAlF4

Abstract
The structural phase transition observed at −13°C in KAlF4 is shown to be martensitic. The results of an investigation of the phonon spectrum by inelastic neutron scattering are reported. It is shown that the transition is preceded by the softening of a flat phonon branch. A model is proposed to explain how such a softening is related to the martensitic transition.